Syntax Assistance Needed

Hello,
I have the following code 
	<xsl:if test="label[.!='']">

I am picking up a project from someone else, and I cannot find the meaning of 
[.!='']
I have searched quite hard to find out what the . means but never found it. Could someone please explain what that means and what the '.' period means. As it is used in quite a few other lines.

eg 	<xsl:when test="item_type[.='user_art']"> 

Thanks,
Scott

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